High-temperature radiator tube design



Nov. 23, 1965 J. E. AHERN HIGH-TEMPERATURE RADIATOR TUBE DESIGN Filed Feb. 14, 1961 IIIIIIIIII' v. 1,1,11,11,14 wag N IIIIIIIIIIIII INVENTOR JOHN E. AHERN w. a. M

A T TORNEV United States Patent 3,219,106 HIGH-TEMPERATURE RADIATOR TUBE DESIGN John E. Ahcrn, Granada Hills, Califi, assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Feb. 14, 1961, Ser. No. 89,577 6 Claims. (Cl. 165-134) This invention relates to high-temperature heat ex changers such, for example, as liquid-metal-to-air radiators, and is particularly concerned with an extended-surface tube element for use in such radiators.

The tubes used in such a high-temperature environment must have high strength at elevated temperatures in order to take all pressure loads. Tubes made of columbium and molybdenum are typical for this application. These materials while exhibiting high strength at high temperatures are subject to catastrophic oxidation at elevated temperatures and must be protected on the air side.

It has been proposed to clad, or coat, the base material, but this has the disadvantage of creating excessive stress due to differential expansion when thermal cycling or thermal shocking the radiator. The resulting stress will cause failure in either the protective cladding or the base metal.

It is an object of this invention to provide an oxidationresistant shield for a tube of a radiator for high-temperature application on the air side of the radiator tube.

A further object of the invention is to provide additional surface per unit length of a radiator tube to increase the air-side heat-transfer rate. This is important in liquid-metal-to-air heat exchangers where the air-side heat-transfer coefficient is so much lower than the liquid side.

A still further object of the invention is generally to improve radiators for use at high temperatures.

These and other advantages and objects of the invention will be evident or will be pointed out in connection with the following description of one embodiment of the invention shown in the accompanying drawings. In these drawings:

FIG. 1 is a side elevation, partly in section, of an end portion of a radiator tube embodying this invention;

FIG. 2 is a transverse section taken on line 22 of FIG. 1;

FIG. 3 is a View of the improved tube installed in a radiator; and

FIG. 4 is a longitudinal, sectional view showing the arrangement of intermediate support areas for the tube.

Referring to the drawings, the radiator tube is made of some suitable material such as columbium or molybdenum. These materials are typical for this application and are capable of resisting elevated temperatures without losing their ability to take the necessary pressure loads. A series of circumferential axially extended grooves 12 are provided in the outer surface of the tube to provide extended surface on the air side of the tube. The grooved sections are separated by ungrooved portions, or lands, 14, one of which is located at each end of the tube and several of which are located intermediate the tube ends. If the tube does not need support intermediate its ends, the grooves can be continuous except at the ends.

In order to prevent catastrophic oxidation at elevated temperatures, each tube is completely surrounded either by a continuous tubular shield 16 or a plurality of short connected shields. Each shield has a corrugated section 18 comprising relatively deep annular corrugations and uncorrugated end portions 20 which fit closely over the outside diameter of tube 10 at the ungrooved portions thereof. The end portions 20 of adjacent shields meet, or very nearly meet, leaving only suflicient space to make 3,219,1fi6 Patented Nov. 23, 1965 the brazed joint between them and the underlying tube 10. As shown in FIG. 1, the corrugations at their inner diameter are in direct contact with the outside diameter of the tube 10. This shield may be made of stainless steel, Monel, Inconel X, or any other suitable material, which can resist oxidation at high temperatures.

The end portions 20 of each shield are either brazed or welded to the smooth annular lands 14 of tube 10 so as to make a fluid-tight seal thereat, and the space between the grooved portion of tube 10 and the corrugated section of the shield is filled with a suitable inert gas to protect the tube from oxidation.

A wear sleeve 22 may be provided over each ungrooved portion 14 of tube 10, as shown in FIGS. 3 and 4, if the tube is so long that it needs support intermediate its ends. This sleeve is brazed or welded to the end portions 20 of adjacent shields, as shown in FIG. 4.

At the ends of the tubes, headers 24 are provided into which the tubes 10 extend and to which the tubular end portions 20 of the adjacent shields also extend and to which they are both welded or brazed.

With this construction the tubes 10 are completely enclosed by the headers and the shields, and oxidation on the air side of the tube is avoided. The corrugated shields are able to slide freely longitudinally of the tube with unrestricted movement due to forces set up by expansion and contraction. The heat-flow pattern is particularly advantageous. Heat is transferred from the liquid metal inside the tube 10 to the tube wall by convection, and then through the tube wall and through the fins provided by the longitudinal grooves by conduction. Heat is transferred from the exterior grooved surface to the interior shield surface by radiation. Conductor resistance through the shield itself will be small and heat will be transferred from the shield exterior to the air by convection. The use of radiant-heat transfer from the exterior grooved surface to the shield is particularly attractive since radiant heattransfer rates increase as a fourth power of the temperature level and thus are significant at elevated temperatures in the range of 1600 F. to 2000 F.

From the above description it will be evident that means has been provided for protecting radiator tubes from oxidation on the air side while avoiding the disadvantages of cladding or coating which has been the practice hereto. It will also be evident that additional surface per unit length of the tube has been provided on the air side to increase air-side heat-transfer rate which is desirable in liquid-metal-to-air heat exchangers where the air-side heattransfer coefficient is very much lower than the coefficient on the liquid side.

It will also be evident that the construction of this invention avoids stresses in the tube structure from stresses set up by expansion and contraction due to differences in temperature in the liquid metal and in the air. Also, means has been provided between the corrugated sections of the tube shield to provide intermediate tube-support areas if they should be required in a long tube.

While only one embodiment of the invention has been shown herein, it will be evident that various changes in the construction and arrangements of the parts may be resorted to without departing from the scope of the invention as defined by the claims; for example, the corrugated shield may be continuous from heater-to-header in some radiators rather than being built in sections as illustrated herein.

I claim:

1. In a tube structure for use in a high-temperature liquid-meta l-to-air radiator, spaced headers, a plurality of tubes extended between said headers, each tube having a plurality of longitudinally grooved sections separated by ungrooved annular lands, and means for protecting said '3 tubes against oxidation comprising tubular shields on each tube extended from header-to-header, said shields being made in sections, each section including smooth cylindrical end portions which overlie and are bonded in fluid-tight manner to adjacent lands and a corrugated portion intermediate said end portions having annular corrugations which overlie a grooved section of said tube.

2. A tube structure as claimed in claim 1 having wear sleeves surrounding the adjacent end portions of adjacent shields and bonded thereto in a fluid-tight manner.

3. A tube structure as claimed in claim 1 having a body of inert gas sealed in the spaces between said grooved sections of said tube and said corrugated portions of said shields.

4. A tube for use in a high-temperature liquid-metal-toair radiator, said tube comprising a continuous length formed of a material having high strength at elevated temperatures and having outer extended surfaces in the form of longitudinal grooves, said grooves being arranged in a plurality of longitudinally spaced circumferential bands which are separated by ungrooved cylindrical lands, and means for protecting said tube from oxidation on its outer air side throughout its alternate grooved and ungrooved portions comprising a plurality of cylindrical shield sections strung on said tube end-to-end along its length, said shield sections having continuous annular corrugations transverse to and longitudinally coextensive with the grooves in said bands and smooth cylindrical end portions coinciding with the lands on said tube, adjacent end portions of adjacent sections engaging closely a land on said tube to which they are sealed in a fluid-tight manner, and a body of inert gas in the space between each shield section and said tube.

5. A tube constructed in accordance with claim 4 in which the small diameter of the corrugations of the shield sections rest on the extremities of the outer grooved surface of the tube.

6. A tube according to claim 4 inwhich the adjacent end portions of adjacent shield sections are enclosed by a wear sleeve which is bonded thereto.

References Cited by the Examiner UNITED STATES PATENTS 1,218,895 3/1917 Porter.

1,495,066 5/ 1924 Browne.

1,920,365 8/1933 Del Mar 257-424 2,155,383 4/1939 Carr 257262.1 X 2,440,245 4/ 1948 Chevigny.

2,686,864 8/1954 Wroughton et al. 207--10.11 X 2,755,925 7/1956 Boccon-Gibod et al. 20710.11 X

ROBERT A. OLEARY, Primary Examiner.

ARTHUR M. HORTON, Examiner. 

1. IN A TUBE STRUCTURE FOR USE IN A HIGH-TEMPERATURE LIQUID-METAL-TO-AIR RADIATOR, SPACED HEADERS, A PLURALITY OF TUBES EXTENDED BETWEEN SAID HEADERS, EACH TUBE HAVING A PLURALITY OF LONGITUDINALLY GROOVED SECTIONS SEPARATED BY UNGROOVED ANNULAR LANDS, AND MEANS FOR PROTECTING SAID TUBES AGAINST OXIDATION COMPRISING TUBULAR SHIELDS ON EACH TUBE EXTENDED FROM HEADER-TO-HEADER, SAID SHIELDS BEING MADE IN SECTIONS, EACH SECTION INCLUDING SMOOTH CYLINDRICAL END PORTIONS WHICH OVERLIE AND ARE BONDED IN FLUID-TIGHT MANNER TO ADJACENT LANDS AND A CORRUGATED PORTION INTERMEDIATE SAID END PORTIONS HAVING ANNULAR CORRUGATIONS WHICH OVERLIE A GROOVED SECTION OF SAID TUBE. 